A Print Shop Has Four Jobs That Have to Be

A print shop has four jobs that have to be processed through their only five-color press. They usually use the first come, first served (FCFS) rule of scheduling jobs. However, the customers are waiting in the lobby for these jobs so the shop wants to minimize the average waiting time. They are going to use the shortest processing time rule to do so. Processing times for each job are as follows (assume this is the arrival order) : Job A, 30 minutes; Job B, 17 minutes; Job C, 12 minutes; and Job D, 39 minutes.
-Using the first come, first served (FCFS) rule to sequence these jobs, the average waiting (flow) time is _____.

A) more than 20 but less than or equal to 30 minutes
B) more than 30 but less than or equal to 40 minutes
C) more than 40 but less than or equal to 50 minutes
D) more than 50 minutes